Stress Dependent Permeability in Low Permeability Gas Reservoirs: Travis Peak Formation, East Texas

Abstract

Abstract This paper identifies factors that control stress dependent permeability in tight gas sandstones of the Travis Peak formation in East Texas, and presents a procedure for prediction of in-situ permeability at any value of net effective stress. Petrophysical analysis of core samples reveals that potential reservoir sandstones can be divided into 3 Rock Types; intervals of rock characterized by a unique response of permeability to stress. The rate of permeability decline with increasing net effective stress is different for each Rock Type and is controlled by three interrelated, pore geometrical parameters -- length, shape and short axis dimension of the pore throats. In these sandstones, permeability reduction is not controlled by the amount of porosity, shale volume, grain size, and volume of authigenic cements (silica, carbonate, and clay). Fundamental controls on pore throat size and shape are grain packing (nature of grain-to-grain contacts) and pore type (primary versus dissolution pores). Rock Type based equations are presented that allow for prediction of permeability and the amount of permeability loss for any value of reservoir stress. The Rock Types can be identified using either laboratory measurement of permeability in core samples at different values of stress, or thin sections of rock samples, including cutting fragments. Algorithms are developed that allow for wireline log identification of each Rock Type using a basic set of log responses (Gamma Ray, Resistivity, Density/Neutron). A knowledge of Rock Type and porosity from wireline logs allows for prediction of permeability at any value of stress through zones of interest in non-cored wells.